There are many types of data storage systems available today. Some of these systems store data cartridges at known locations, and retrieve desired data cartridges from the known locations so that data may be written to or read from the data cartridges. Such data storage systems are often referred to as “juke box” data storage systems, particularly if they can accommodate a large number of data cartridges.
A typical juke box data storage system may include one or more different types of cartridge receiving devices for holding the various data cartridges. For example, one type of cartridge receiving device may comprise a cartridge storage rack or “magazine”, while another type of cartridge receiving device may comprise a cartridge read/write device or “drive”. The cartridge storage racks or magazines serve to provide storage locations for the data cartridges and are often arranged so that they form one or more vertical stacks, although other configurations are possible. The cartridge read/write device may be located at any convenient location within the data storage system.
The data storage system may also be provided with a movable cartridge engaging assembly or “picker” for transporting the data cartridges between the various cartridge receiving devices (e.g., between the cartridge storage racks and the cartridge read/write devices). A typical cartridge engaging assembly may also be provided with a plunge mechanism or “thumb assembly” for engaging the various data cartridges contained in the cartridge receiving devices and for drawing them into the cartridge engaging assembly. A positioning system associated with the cartridge engaging assembly may be used to move the cartridge engaging assembly between the various cartridge receiving devices.
Data storage systems of the type described above are usually connected to a host computer system which may be used to access or store data on the data cartridges. For example, if the host computer system issues a request for data contained on a particular data cartridge, a control system associated with the data storage system will actuate the positioning system to move the cartridge engaging assembly along the cartridge storage racks until the cartridge engaging assembly is positioned adjacent the desired data cartridge. The plunge mechanism associated with the cartridge engaging assembly may then extend to remove the data cartridge from its cartridge storage rack, and then retract to draw the cartridge into the cartridge engaging assembly. The positioning system may then be actuated to move the cartridge engaging assembly to an appropriate cartridge read/write device. Once properly positioned adjacent the cartridge read/write device, the plunge mechanism may extend to insert the selected data cartridge into the cartridge read/write device so that the host computer may thereafter read data from or write data to the data cartridge. After the read/write operation is complete, the plunge mechanism may be actuated to remove the data cartridge from the cartridge read/write device. The cartridge engaging assembly may thereafter return the data cartridge to its cartridge storage rack.
A typical plunge mechanism is usually slidably mounted to the cartridge engaging assembly and is provided with a drive system so that the plunge mechanism may be moved toward and away from a cartridge access end of the cartridge engaging assembly (i.e., to an extended or retracted position). For example, if it is desired to retrieve a data cartridge from a cartridge receiving device, the drive system moves the plunge mechanism toward the cartridge access end of the cartridge engaging assembly so that the plunge mechanism may engage (or grab) the data cartridge. The drive system then retracts the plunge mechanism and pulls the engaged data cartridge into the cartridge engaging assembly. If it is desired to load the data cartridge into the cartridge receiving device, the drive system then moves the plunge mechanism and data cartridge toward the cartridge access end of the cartridge engaging assembly, thus inserting the data cartridge into the cartridge receiving device.
Typically, the position of the plunge mechanism must be controlled within fairly tight tolerances, especially when the plunge mechanism is moved to its extended position. Otherwise, the plunge mechanism may not be able to adequately engage a data cartridge, or the plunge mechanism may fail to seat a data cartridge in a cartridge receiving device. One method of controlling the position of a plunge mechanism is disclosed in U.S. Pat. No. 6,104,693, entitled “Mounting System for Cartridge Plunge Mechanism”, which is hereby incorporated by reference for all that it discloses. The method disclosed therein uses a detector assembly to read a plurality of index marks on an elongate linear reference member. The detector assembly is mounted to the body of a plunge mechanism, and the reference member is mounted to the frame of the cartridge engaging assembly. In this manner, movement of the plunge mechanism causes the detector assembly to pass by the plurality of index marks on the reference member. The position of the plunge mechanism may therefore be controlled, for example, by counting the number of index marks which the plunge mechanism passes, and controlling the drive system for the plunge mechanism in response thereto.